Suppression of glucose absorption by some fractions extracted from Gymnema sylvestre leaves

Extracts containing gymnemic acids, which were extracted from the leaves of Gymnema sylvestre (GS) as nine fractions, were evaluated for their effects on a high K(+)-induced contraction of guinea-pig ileal longitudinal muscles, on glucose transport mediated by the difference of glucose-evoked transmural potential difference (delta PD) in the inverted intestine of guinea-pig and rat, and on blood glucose in rat. Among nine fractions obtained by high performance liquid chromatography from the extract, f-2 and f-4 strongly suppressed the high K(+)-induced contraction of the ileal muscle, f-3 and f-5 did so moderately, and f-8 and f-9 did so weakly, whereas the other fractions did not affect it. The degree of suppression of high K(+)-induced contraction by f-2 at 74% was almost the same as that of f-4 at 67%, at concentrations of 0.1 mg/ml. The suppressed contraction by f-2 or f-4 was recovered by adding 5.5 mM pyruvate. The delta PD increased by 5.5 mM glucose in the inverted intestines of guinea-pig and rat were equally suppressed by 0.1 mg/ml of f-2 or f-4 to 40%. In a rat sucrose tolerance test, f-2 and f-4 suppressed the elevation of blood glucose level. Both f-2 and f-4 suppressed the contraction of guinea-pig ileal longitudinal muscle, interfered with the increase in delta PD induced by glucose in the inverted intestines of guinea-pig and rat, and inhibited the elevation of blood glucose level. In conclusion, it is suggested that some of the extracts containing gymnemic acids from GS leaves suppress the elevation of blood glucose level by inhibiting glucose uptake in the intestine.